Surprising Find: Live Bacteria Help Create Rain, Snow & Hail

Below:

Next story in Science

Living bacteria that get whipped up into the sky may be just the
spark needed for rain, snow and even hailstorms, research now
finds.

Alexander Michaud of Montana State University in Bozeman, Mont.,
found large amounts of bacteria at the centers of giant
hailstones.

Traditionally, researchers have thought that minerals or other
particulates in clouds caused water droplets to glom together
until they were large enough to fall as raindrops, snowflakes and
hail. The new research shows that a large variety of bacteria,
and even fungi, diatoms and algae, persist in the clouds and can
be
used as precipitation starters, a growing field of study
called bioprecipitation. (In order for snow, say, to fall from
clouds, particles around which ice crystals can form — called ice
nuclei — are needed.)

"Minerals were thought to be the dominant ice nucleators in the
atmosphere, but they aren't nearly as active as biological
particles," said Brent Christner, a microbiologist studying
bioprecipitation at Louisiana State University who is presenting
the work today (May 24) at the General Meeting of the American
Society for Microbiology in New Orleans.

Bacterial beginnings

For minerals to
form ice nuclei, water needs to be much colder than is
usually found in clouds, Christner told LiveScience. Bacteria and
other living particles that get swept up into the sky may serve
as alternative nucleators.

Michaud, also presenting at the conference, collected hailstones
about the size of golf balls (greater than 2 inches, or 5
centimeters, in diameter) after a
huge hailstorm hit Montana in June 2010. He separated the
hail into four layers, which are formed as the ice is created and
moves up and down through the clouds, accumulating layer upon
layer of ice. He found that bacteria levels were highest at the
core of the hail.

"Bacteria have been found within the embryo, the first part of a
hailstone to develop. The embryo is a snapshot of what was
involved with the event that initiated growth of the hailstone,"
Michaud said in a statement. "There is growing evidence that
these nuclei can be bacteria or other biological particles."

By determining the temperature at which the hailstones formed,
the team found that these bacteria allowed the ice to form at
warmer temperatures than otherwise expected.

Importance of ice

Previously Christner's group found that the widely studied plant
pathogen Psuedomonas syringae plays an important role in
snow formation all over the world, including Antarctica, where
there are few plants. The pathogen is known to be
very good at creating ice at temperatures above the normal
freezing point of water.

These bacteria are equipped with a special substance that binds
water molecules in an orderly arrangement, and in these
proximities they can more easily form ice particles. When on the
ground, the bacteria use this ice to damage plants, causing the
plant cells to break apart and allowing the bacteria to enter.

"An organism that lives on a plant, where you want to be is back
on the ground on another plant. If you have the ability to
produce precipitation, fall down and land on a plant, it could be
a cycle," Christner told LiveScience. "They could be using this
protein as a way to hitchhike on the water cycle."